The present invention relates generally to methods for sampling one or more physiological signals from a patient. More specifically, the present invention relates to long term, ambulatory monitoring of one or more neurological signals from a patient using a minimally invasive methods.
Epilepsy is a disorder of the brain characterized by chronic, recurring seizures. Seizures are a result of uncontrolled discharges of electrical activity in the brain. A seizure typically manifests itself as sudden, involuntary, disruptive, and often destructive sensory, motor, and cognitive phenomena. Seizures are frequently associated with physical harm to the body (e.g., tongue biting, limb breakage, and burns), a complete loss of consciousness, and incontinence. A typical seizure, for example, might begin as spontaneous shaking of an arm or leg and progress over seconds or minutes to rhythmic movement of the entire body, loss of consciousness, and voiding of urine or stool.
A single seizure most often does not cause significant morbidity or mortality, but severe or recurring seizures (epilepsy) results in major medical, social, and economic consequences. Epilepsy is most often diagnosed in children and young adults, making the long-term medical and societal burden severe for this population of patients. People with uncontrolled epilepsy are often significantly limited in their ability to work in many industries and usually cannot legally drive an automobile. An uncommon, but potentially lethal form of seizure is called status epilepticus, in which a seizure continues for more than 30 minutes. This continuous seizure activity may lead to permanent brain damage, and can be lethal if untreated.
While the exact cause of epilepsy is often uncertain, epilepsy can result from head trauma (such as from a car accident or a fall), infection (such as meningitis), or from neoplastic, vascular or developmental abnormalities of the brain. Most epilepsy, especially most forms that are resistant to treatment (i.e., refractory), are idiopathic or of unknown causes, and is generally presumed to be an inherited genetic disorder.
While there is no known cure for epilepsy, the primary treatment for these epileptic patients are a program of one or more anti-epileptic drugs or “AEDs.” Chronic usage of anticonvulsant and antiepileptic medications can control seizures in most people. An estimated 70% of patients will respond favorably to their first AED monotherapy and no further medications will be required. However, for the remaining 30% of the patients, their first AED will fail to fully control their seizures and they will be prescribed a second AED—often in addition to the first—even if the first AED does not stop or change a pattern or frequency of the patient's seizures. For those that fail the second AED, a third AED will be tried, and so on. Patients who fail to gain control of their seizures through the use of AEDs are commonly referred to as “medically refractory.”
For those patients with infrequent seizures, the problem is further compounded by the fact that they must remain on the drug for many months before they can discern whether there is any benefit. As a result, physicians are left to prescribe AEDs to these patients without clear and timely data on the efficacy of the medication. Because these drugs are powerful neural suppressants and are associated with undesirable side-effects and sedation, it is important to minimize the use and dosage of these drugs if the patient is not experiencing benefit.
A major challenge for physicians treating epileptic patients is gaining a clear view of the effect of a medication or incremental medications. Presently, the standard metric for determining efficacy of the medication is for the patient or for the patient's caregiver to keep a diary of seizure activity. However, it is well recognized that such self-reporting is often of poor quality because patients often do not realize when they have had a seizure, or fail to accurately record seizures. In addition, patients often have “sub-clinical” seizures where the brain experiences a seizure, but the seizure does not manifest itself clinically, and the patient has no way of making note of such seizures.
Demographic studies have estimated the prevalence of epilepsy at approximately 1% of the population, or roughly 2.9 million individuals in the United States alone. In order to assess possible causes for the seizures and to guide treatment for these epileptic patients, epileptologists (both neurologists and neurosurgeons) typically admit the patient to an epilepsy monitoring unit (“EMU”), where the patient will undergo continuous video-EEG monitoring in an attempt to capture ictal brain activity (“seizure activity”) and interictal brain activity.
During their stay in the EMU, the patients may be purposefully stressed in an attempt to induce seizure activity. For example, the patients are often sleep deprived, and if the patients are on medication, the medications may be decreased or stopped. However, for patients who have infrequent seizures, even in such a stressed state, many of such patients do not have a seizure during their stay in the EMU, and such costly and time consuming in-hospital monitoring provides little or no insight into the patient's condition.
While in-patient video-EEG monitoring is currently the standard of care, improvements are still needed. For example, one drawback that has not been addressed by video-EEG monitoring is the fact that the sleep deprivation and/or a decrease or complete stoppage of the AEDs may cause cluster seizures and/or induce status epilepticus—which may not be reflective of the patient's typical seizures or seizure frequency. Thus, the EEG data that is collected in the EMU may not accurately reflect the patient's condition—which can complicate attempts to diagnose and properly treat the patient.
Consequently, what are needed are methods and systems that are capable of long-term, out-patient monitoring of epileptic patients. It would further be desirable if the long-term monitoring could be processed into appropriate metrics that can quantify the clinical benefit of the medication or other therapies. It would also be desirable to have system that could record seizure activity, to enable the meaningful study of patients with infrequent seizures.